In order to enlarge a negative of a predetermined format, for example, to enlarge a negative having a size of 24 .times. 36 millimeters to a negative having a size of 60 .times. 70 millimeters, it is necessary to exchange not only a magnifying lens but also the condenser. For this reason, in a known enlarger the aforesaid condenser in a necessarily required light-deflection mirror is disposed in a single housing, when the projection or enlargement lamp is arranged horizontally, the housing being exchangeable from the top side of the projection head. The insert member abuts against a stop in the projection head itself. To permit exact abutment of a negative or film against the condenser, or against an opaque disc disposed between the condenser and the film or negative, a special mechanism is provided, which presses the film trap, or the carrier of the film, or negative, upon insertion of the film into the condenser.
Such a special mechanism for displacement in a vertical direction of the film trap, or the carrier of the film, in conjunction with the mechanism facilitating the exchange of the condenser system from the top side of the projection head, is not inexpensive.